SAE AS417

Description / Abstract: This Standard covers air data equipment (hereinafter designated the instrument) which when connected to sources of aircraft electrical power, static pressure, total pressure and outside air temperature (singly or in combination) provides some or all of the following computed air data output signals:

Pressure Altitude*

Pressure Altitude (Reporting)

Baro-Corrected Pressure Altitude*

Vertical Speed*

Computed Airspeed*

Mach Number*

Maximum Allowable Airspeed*

Static Air Temperature (*when used as an alternate for total temperature)

Total Temperature*

Altitude Rate

Overspeed Warning

Altitude Hold

Airspeed Hold

Mach Hold

q_c (impact pressure)

True Airspeed

Others

Limits:

Full scale outputs marked with an asterisk may supply required pilots flight instruments as specified in Federal Aviation Regulations (e.g., Part 25, paragraph 25.1303) and when so used, shall meet the minimum accuracy requirements of Paragraph 4 of this document (AS 417A). Other outputs of the same function, signal characteristic and similar usage such as flight recorder altitude may have an added "correspondence tolerance" which shall not exceed 50% of the minimum standard tolerance unless otherwise specified by existing Federal requirements.

Those outputs supplied to other subsystems for scheduling purposes are not the concern of this minimum performance specification but should be reviewed for compatibility in the particular installation.

The above outputs shall include correction for certified static source errors as provisioned and matched to the characteristics of the particular type and model aircraft in which the instrument is intended to be used. The tolerances expressed in Paragraph 4 include the allowance for static source error corrections up to ± 300 ft for any altitude-airspeed combination. Necessity for greater error correction requires special review and approval of tolerances based on the installation.

Those outputs intended for particular using subsystems and being either of a discrete, incremental, or rate characteristics and not covered by 2.1.1 above shall meet the specific requirements for the respective category of output as may apply in Paragraph 4 with no added correspondence allowance where accuracy is concerned for duplicate outputs.

The instrument shall not be damaged by having applied to its pressure fittings any of the following pressures singly or in combination: Static Pressure Fitting - Approximately 1.4 inch Hg Abs to 37 inch Hg Abs. Total Pressure Fitting - Approximately 0 inch Hg Abs to 50 inch Hg Abs, with the additional provision that the instrument shall not be required to withstand an excess of Total over Static Pressure of more than 19 inch Hg, nor an excess of Static over Total Pressure of more than 2 inch Hg.

In the event that the above limits are likely to be exceeded, Transducer over Pressure protection shall be provided by the user.